Surface-coated metal material having resistance to molten tin

ABSTRACT

A metal material having corrosion resistance against molten tin, said metal material comprising a metal base having iron as a main constituent and a surface coating alloy layer, said surface coating alloy layer composed of an iron alloy and a particulate matter dispersed in said alloy, said alloy consisting of iron and one or both of titanium and aluminium, said particulate matter consisting essentially of at least one of TiO2, Al2O3, ZrO2, CaO, MgO, SrO, BaO and SiO2 and one or both of titanium and aluminium. The metal material is prepared by contacting a powdery mixture of one or both of titanium and aluminium and at least one metal oxide listed above with a metal base having iron as a main constituent, and heating them to an elevated temperature in an inert atmosphere.

United States Patent [1'91 Itakura et a].

' 1111 3,771,974 [451 Nov. 13, 1973 SURFACE-COATED METAL MATERIAL HAVINGRESISTANCE TO MOLTEN TIN [75] Inventors: K'iyoshi ltakura, Nishinomiya;

Yutaka Ohmae, Kawanishi, both of I Japan [73] Assignee: Nippon SheetGlass Co., Ltdt,

Osaka, Japan [22] Filed: Sept. 8, 1970 [21] Appl. No.: 70,066

[30] Foreign Application Priority Data Sept. 18, 1969 Japan 44/71126Sept. 18, 1969 Japan 44/71127 [52] US. Cl. 29/195 M, 117/107.2 P

[51] Int. Cl B32]: 15/18 [58] Field of Search 29/195 M [56] ReferencesCited UNITED STATES PATENTS 1,775,531 12/1956 Montgomery et a1. 29/195 X2,900,276 8/1959 Long et a1 29/195 X Primary ExaminerL. Dewayne'RutledgeAssistant ExaminerE'. L. Weise Attorney-Wenderoth, Lind & Ponack [57]ABSTRACT A metal material having corrosion resistance against moltentin, said metal material comprising a metal base having iron as a mainconstituent and a surface coating alloy layer, said surface coatingalloy layer composed of an iron alloy and a particulate matter dispersedin said alloy, said alloy consisting of iron and one or both of titaniumand aluminium, said particu late matter consisting essentially of atleast one of TiO A1 0 ZrO CaO, MgO, SrO, BaO and SiO and one or both oftitanium and aluminium. The metal ma- V terial is prepared by contactinga powdery mixture of one or both of titanium and altiminium and at leastone metal oxide listed above with a metal base having iron as a mainconstituent, and heating them to an elevated temperature in an inertatmosphere.

4 Claims, 1 Drawing Figure SURFACE-COATED METAL MATERIAL HAVINGRESKSTANCE T MOLTEN TIN This invention relates to a surface-coated metalmaterial having resistance to molten metal, especially mol ten tin.

in recent years, the glass industry developed a method of producingglass sheet having good flatness by pouring out a molten glass melted ina glass-melting furnace continuously over a molten metal to form a glassribbon, cooling it by advancing it along a molten metal bath, and thenwithdrawing it. This method is termed a float glass process in the art.In this process, a molten tin is mainly used as the molten metal, and ispalced in a tank of refractory brick. The atmosphere surrounding themolten metal bath is a reducing atmosphere for preventing the oxidationof the metal bath. Because of oxygen and sulfur contained in very smallamounts in the glass batch or in the atmosphere, small amounts of oxidesand sulfides are formed on the molten metal bath, and adhere to theunderside of the glass ribbon advancing on the molten metal bath whilebeing in contact therewith, thereby causing defects on the glass ribbon.A pocket is provided on the side wall of the molten metal bath to removea floating matter comprising these oxides and sulfides; the floatingmatter is gathered in the pocket and then scraped out. This scrapingmeans is partly immersed in the molten metal, and undergoes strongcorrosion of the molten metal. Of course, any other materials which arein contact with the molten metal undergo strong corrosion of the moltenmetal. Hence, the material to be immersed in the molten metal need behighly anti-corrosive against the molten metal, and readily processablemechanically, and have high strength and thermal stability at hightemperatures. Silicon nitride and graphite (in a reducing atmosphere)can be mentioned as such material from the standpoint of resistance toheat and corrosion, but these materials meet with difficulty in respectof processability and mechanical strength. Stainless steel is a materialwhich is easily workable and heat resistant and has strength at hightemperatures, but has the de fect of being susceptible to corrosion bythe molten metal.

Generally, even alloys having good thermal stability and corrosionresistance in use in the air do not necessarily have corrosionresistance when being in contact with a molten tin. For instance,platinum and gold are said to be excellent in heat resistance andcorrosion resistance in the air, but when immersed for a day in moltentin at 600C., undergo large corrosion. With stainless steelheat-resistant alloys such as l8Cr-8Ni stainless steel or 25 Cr- Nistainless steel, the main constituents such as nickel, chromium and ironare locally dissolved out and finally disappear when such alloys areimmersed in molten tin for a day at 900C. In choosing materialsresistant to molten tin, therefore, we cannot rely on the standards forordinary heat-resistant and corrosion-resistant materials.

It has now been found that iron-aluminium alloys, iron-titanium alloys,iron-aluminium-titanium alloys and the like have good corrosionresistance against molten tin, and that when the surface of a metalconsisting predominantly of iron is subjected to calorization, a kind fothe aluminium impregnation method, the corrosion resistance of the metalto molten tin can be enhanced. The calorization is a well-known methodof treating the surface of metal which involves packing the metal to betreated into an iron receptacle together with a penetrant consisting ofthe powders of an aluminium-iron (:50) alloy and a small amount ofammonium chloride, and after sealing, heating the receptacle to 900l,O00C. thereby to form a coating of the iron-aluminium alloy on thesurface of the metal. A marked increase in corrosion resistance isobserved when the calorizing treatment is applied especially to suchalloys as iron-aluminium, iron-titanium, and ironaluminium-titaniumalloys. The corrosion resistances of 5Al-95Fe alloy, 5Ti9SFe alloy and5Al-9Ti-86Fe alloy (the alloy composition being by weight) wereexamined, and the results are shown in Table 1 below. The test procedurewas as follows: The metal material was immersed in molten tin at 970C.in a reducing atmosphere, and the number of days which elapsed untilthere was a corrosion perceptible to the naked eye on the surface of thematerial.

TABLE 1 Materials Not calorized Calorized 5Al-9SFe alloy 7 days 25 days5Ti-95Fe alloy 7 25 5Al-9Ti-86Fe alloy 8 29 It is clearly seen from theresults shown in Table 1 that these alloy materials have corrosionresistance durable for about 25 days when calorized. The corrosionresistance of this degree, if not sufficient, is feasible for practicalpurposes. These three types of iron base alloys, however, are expensivein addition to having such defects as extreme hardness and difficulty ofworking. Mild steel and stainless steel which are easy to workmechanically will have an improved corrosion resistaiice when calorized,but the corrosion resistance is durable for less than 7 days, as will beshown later in the Examples. It is necessary therefore to replace suchmaterials frequently.

An object of the present invention is to provide a metal material whichhas a high resistance to corrosion by molten tin and high strength andthermal stability at high temperatures and which is easy to workmechanically.

According to this invention, there is provided a metal material havingcorrosion resistance against a molten metal consisting predominantly oftin, said metal material comprising a metal base having iron as a mainconstituent and a surface coating alloy layer, said surface coatingalloy layer composed of an iron alloy and a partieulate matter dispersedin said alloy, said alloy consisting essentially of iron and at leastone metal selected from the group consisting of titanium and aluminium,said particulate matter consisting of at least one metal oxide selectedfrom the group consisting of TiO Al- 0 ZrO CaO, MgO, SrO, BaO and Si0and at least one metal selected from the group consisting of titaniumand aluminium.

By the term metal base having iron as a main constituent or metal baseconsisting predominantly of iron are meant such ordinary iron materialsas cast iron, carbon steel, stainless steel, manganese steel, chromiumsteel, and tungsten steel and also such special iron alloys as Al-Fealloy, Al-Ti-Fe alloy and Ti-Fe alloy. The term molten metal consistingpredominantly of tin or molten metal having tin as a main constituentmeans tin or tin alloys as molten metal used in the float glass process.

The excellent corrosion resistance against molten tin exhibited by themetal material of the present invention having a surface coating layeris considered to be due to the fact that the iron-titanium alloy layer,ironaluminium alloy layer or iron-titanium-aluminium alloy layer whichitself has corrosion resistance against molten tin is maintained forlong periods of time on the surface or the base by the presence of theparticulate matter. The titanium and/or aluminium, the constituents ofthe surface coating alloy layer diffuse into the inside of the metalbase having iron as a main constituent during use in a high temperaturemolten tin. When the concentration of the titanium and/or aluminium inthe coating alloy layer is reduced and the corrosion resistance of thecoating alloy layer against the molten tin is about to decrease, thetitanium and/or aluminium present in the particulate matter dispersed inthe coating alloy layer diffuse into the alloy layer to restrain thelowering of the concentration of the titanium and/or aluminium in thealloy layer. Thus, the surface coating alloy layer having corrosionresistance is maintained for a prolonged period of time. Since the metaloxides containing the particulate matter are chemically stable at hightemperatures to such metal components as tin and iron present around theparticulate matter, the particulate matter containing the metal oxidesare hardly corroded by the molten tin. Moreover, by the dispersion ofthe particulate matter in the alloy layer, the net surface area of thealloy part of said layer in contact with molten tin decreases, and thecorrosion resistance is further enhanced.

Any metal oxides can be used in the present invention which arechemically stable to the metal components such as tin and iron existingaround the particulate material, at high temperatures (600-1l00C.). Fromthe standpoint of feasibility, economy and ease of handling, the use ofA1 0,, TiO ZrO CaO, MgO, SrO, BaO and SiO as the metal oxides containedin the particulate matter is particularly preferred.

As previously stated, the particulate matter present in the coatingalloy layer of the present invention is stable to molten tin, andreduces the surface area of the alloy part of said layer in contact withthe molten tin and serves to supply titanium and/or aluminium componentto the alloy layer. Therefore, that part of the particulate matter whichis present near the surface of the coating alloy layer acts effectively.

One preferred embodiment of the corrosion-resistant metal material ofthe present invention is a metal material in which the particulatematter is present only on the surface part of an alloy layer of iron andtitanium and/or aluminium and is substantially absent in the deeper partof the alloy layer. Another preferred mode of the metal material of thisinvention is a metal material in which the composition of the surfacecoating alloy layer on the base material is not uniform,and theconcentration of titanium and/or aluminium is progressively lower fromthe surface part towards thepart in contact with the base material. Itis assumed that by such a concentration gradient, the bonding betweenthe alloy layer and the base material will become firm.

ln order for the surface-coated metal material of this invention toexhibit overall good properties such as corrosion resistance againstmolten tin, mechanical workability, strength, and thermal stability, thecoating layer contain the particulate matter only near its surface, andthis part containing the particulate matter have a thickness of at least30 11.. Furthermore, the alloy layer at its surface portion containingthe particulate matter desirably contains 5-50 percent by weight ofiron, 40-90 percent by weight of titanium, zirconium, calcium,magnesium, aluminium, strontium, barium and/or silicon, and 23-12percent by weight of oxygen in the form of oxide, as a total amount ofthe alloy and the particulate matter.

The particulate matter preferably has a diameter mainly in the range of10 to 100 u, and preferably consists of 15-55 percent by weight of metaloxides, and -85 percent by weight of titanium and/or aluminium metals.The ratio of the particulate matter mixed in the surface portion of thealloy layer is preferably 15-45 percent calculated as the percentage ofthe sectional area-of the particulate based on the total sectional areanear the'surface of the alloy layer.

The corrosion-resistant metal material of this invention has corrosionresistance more than that of calorized iron-aluminium-titanium alloy,iron-aluminium alloy or iron-titanium alloy. It is easy to workmechanically and is low in cost.

The surface-coated metal material of this invention having corrosionresistance against molten metal is produced by contacting a mixtureconsisting of the powders of at least one metal selected from the groupconsisting of titanium and aluminum and the powders of at least onemetal oxide selected from the group consisting of TiO,, A1 0,, ZrO CaO,MgO, SrO, BaO and SiO with a metal base consisting predominantly ofiron, and beating them to an elevated temperature in an inertatmosphere. In this process, the metal base consisting predominantly ofiron reacts with the surrounding mixture of the powders of titaniumand/or aluminium and the powders of metal oxides, and the titaniumand/or aluminium actively diffuses and penetrate into the metal base toform an alloy. This results in the production of an alloy layer of ironand aluminium and/or titanium on the surface of the metal base, and aparticulate matter consisting substantially of the metal oxides andtitanium and/or aluminium is dispersed in the alloy layer at the sametime. By the term inert atmosphere" is meant an atmosphere filled with agas of the class which does not substantially oxidize the powders oftitanium and aluminium to be contacted with the metal base, and does notsubstantially reduce the metal oxide powders.

Prior to contacting of the metal base having iron as a main constituentwith the powdery mixture of the metal oxides and titanium and/oraluminium in the above-mentioned process, the base metal may bepretreated by coating a thin layer of a metal oxide on it, immersing itin molten aluminium, or bonding a thin layer of aluminium by the spraymethod. This pretreatment is particularly effective for applying ahomogeneous coating layer to the surface of the metal base. It isdesired that the powdery mixture described should consist of 65-90percent by weight of the metal oxides and 10-35 percent by weight oftitanium and/or aluminium. The heating temperature need be below a pointat which the base metal begins to be deformed, and generally the desiredrange is from 750 to l,lC. The treating time is generally about 1 to 10hours, but the employment of high frequency heating makes it possible toshorten the treating time to several minutes.

The present invention will be described further by the followingExamples in which all percentages are by weight.

EXAMPLE 1 A ca. 4 percent aqueous starch paste solution containingpercent of alumina powders having a size of 10-60 was coated in a thinlayer on the surface of a round rod of mild steel, 13Cr stainless steel,18Cr 8Ni stainless steel, and 25Cr 2ONi stainless steel each having anouter diameter of 10 mm and a length of 100 mm, and dried. Each of theround rods was embedded in a heating chamber containing 25 percent ofaluminium powders having a size mainly in the range of 5 y. to 10 p. and75 percent of alumina powders having a size of not more than 60 u, andwhile filling the chamber with argon gas, the round rod was heated for 6hours at a temperature of 950C. After allowing the rod to cool, it waswithdrawn from the powder in the heating chamber, and the powderadhering to its surface was removed by brushing. There was obtained ametal material having as a surface coatinglayer on the base material, alayer of iron-aluminium alloy in which the particulate matter consistingof aluminium and alumina was dispersed.

The mild steel-base metal material contained a surface coating alloylayer having a thickness of about 0.7 mm, and an area having theparticulate matter dispersed existed between the surface and the pointabout 0.2 mm deep from the surface in the alloy layer. When thestainless steels such as 13 Cr stainless steel, 18%Cr*8%Ni stainlesssteel, and 25%Cr2%Ni stainless steel were used as the base metal, thethickness of the surface coating was about 0.5 mm, hardly differing fromsteel to steel. An area having the particulate matter dispersed waspresent between the surface and a point about 015mm deep from thesurface in any of these products.

The coating alloy layers of the metal materials obtained in this Examplehad substantially the same structure although differing more or less inthickness depending upon the type of the base metal. Therefore, thestructure of the coating alloy layer was observed using the metalmaterial having mild steel as the base. This will be discussed somewhatin detail below with reference to the attached microscopic photograph.

As is shown in the microscopic photograph, a coating alloy layer 1 issuperposed on a base material 4 in intimate contact with each other inthe corrosion-resistant metal material of this invention. The alloylayer consists of an upper layer 2 in which a particulate matter isdispersed in the alloy and a lower area 3 substantially free from theparticulate matter and consisting. only of an iron-aluminium alloy. Inthis photograph, the thickness of the layer 1 is about 700 ,u, and thearea 2 has a thickness of about 200 u. The ratio of the particulatemixed in the area 2 is about 35 percent calculated as the percentage ofthe sectional area of the particulate matter based on the totalsectional area taken near the surface. According to the measurement ofan X-ray microanalyzer, the composition of the aluminium-iron alloylayer of the area is 54 percent aluminium and 46 percent iron. Thiscorresponds substantially to the composition Fe Al The particulatematter has a size mainly in the range of 10 u to 100 ,u, and consists ofabout 55 percent aluminium and about 45 percent alumina. In the area 3where the particulate matter is not dispersed, the concentration ofaluminium is reduced progressively towards the base material 4, andfinally, the area 3 is firmly bonded to the base material 4.

The four corrosion-resistant metal materials obtained in this Examplewere each immersed in molten tin at 970C. in a reducing atmosphere, andthe number of days which elapsed until the occurrence of corrosion onthe surface was determined with the naked eye. It was found as shown inTable 2 below that irrespective of the type of the base material, all ofthe metal materials did not undergo appreciable corrosion even after 60days from the immersion. For comparative purposes, Table 2 also givesthe corrosion test results on the untreated base material and thecalorized base material.

TABLE 2 Number of days elapsed until the occurrence of appreciablecorrosion Base materials Untreated Calorized Metal material obtained inthis Example Mild steel 2 hours 5 days more than 60 days 13%Cr stainless6 hours 7 days more than steel 60 days 18%Cr-8%Cr 4 hours 6 days morethan stainless steel 60 days 25%(Jr-20%Ni 4 hours 6 days more thanstainless steel 60 days EXAMPLE 2 A ca. 4 percent aqueous starch pastesolution containing 10 percent of titanium oxide powders having a sizeof 10-60 p. was coated in a thin layer on the surface of each of thesame round rods as set forth in Example 1, and dried. Each of the roundrods was then embed tied in a heating chamber containing percent oftitanium oxide powders having a size of not more than 60 p, and 25percent of titanium powders having a size mainly in the range of 5 y. to10 .1.. While filling the chamber with argon gas,the round rod washeated for 10 hours at l,l00C. After allowing the rod to cool, it waswithdrawn from the powder in the'heating chamber, and the powderadhering to its surface was removed by brushing. There was obtained asurfacecoated metal material having as a surface coating layer on thebase material, a layer of iron-titanium alloy in which the particulatematter consisting of titanium and titanium oxide was dispersed.

Each of the metal materials obtained was subjected to the same corrosionresistance test as set forth in Example l, and it was found that evenafter a lapse of 60 days none of the four metal materials obtainedunderwent corrosion.

The surface coating layer of the metal material having mild steel as thebase metal had a thickness of about 0.4 mm, and an area having theparticualte matter dispersed therein was present between the surface anda point about 0.1 mm deep from the surface in the alloy layer. In thecase of 13%Cr stainless steel, 18%Cr- 8%Ni stainless steel, and25%Cr-20%Ni stainless steel, the thickness of the surface coating wasabout 0.3, hardly differing from steel to steel. An area having theparticulate matter dispersed therein was present between the surface anda point about 0.08 mm deep from the surface in the alloy layer.

The mild steel-base metal material obtained will be discussed.Thethickness of the alloy layer of this metal material is about 400 pt,and the particulate matter is dispersed in an area existing between thesurfat ie and a point about 100 1. deep from the surface in the alloylayer. The ratioof the particulate material mixed in' this area wasabout 30 percent as the percentage of the sectional area of theparticulate matter based on the total sectional area. According to themeasurement of an X-ray microanalyzer, the iron-titanium alloy layer inthe area where the particulate matter is dispersed consists of 65percent titanium and 35 percent iron, which substantially corresponds tothe composition Ti Fe. The main size of the particulate matter is -80,4, and its composition is about 55 percent titanium and abour 45percent titanium oxide. The concentration of titanium is reducedprogressively towards the base metal in the area not having theparticulate matter dispersed which exists between the area having theparticulate matter dispersed and the base metal, and finally, the alloylayer is firmly bonded to the base metal.

EXAMPLE 3 Each of the same round rods as used in Example 1 was embeddedin a heating chamber containing 75 percent of calcium oxide powdershaving a size of not more than 60 p. and 25 percent of aluminium powdershaving a size of 10-60 p.. While filling the heating chamber with argongas, the rod was heated for 6 hours at 900C. After allowing the rod tocool, it was withdrawn from the powders in the heating chamber, and thepowders adhering to the surface were removed by brushing. There wasobtained a surface-coated metal materials having as a coating layer onthe surface of the base material, an iron-aluminium alloy layer in whichthe particulate matter consisting of aluminium and calcium oxide wasdispersed.

Each of the metal materials obtained in this Example was subjected tothe same corrosion resistance test as set forth in Example 1, and it wasfound that even after a lapse of 60 days, these metal materials did notundergo appreciable corrosion.-

The thickness of the alloy layer of the metal material containing mildsteel as the base metal was about 0.65 mm, and an area having theparticulatematter dispersed therein was present betw'een'the surface anda point about 0.2 mm deep from the surface. The thickness of the coatingalloy layer in the 13%Cr stainless steel, l8%Cr8%Ni stainless steel and25%Cr-20%Ni stainless steel was about 0.5 mm, hardly differing fromsteel to steel, and an area having the particulate'matter dispersedtherein was present between the surface and a point about 0.15 mm deepfrom the surface.

EXAMPLE 4 Each of the four round rods same as used in Example 1 wasembedded in a heating chamber containing 75 percent of calcium oxidepowder having a size of not more than 60 u and 25 percent of the powdersof titanium having a size mainlyin the range of 10 p. to 60 a. Whilefilling the heating chamber with argon gas, each of the rods was heatedfor 8 hours at 1,I00C. After allowing the rod to cool, it was withdrawnfrom the powders in the heating chamber, and the powders adhering to thesurface were removed by brushing. There was obtained a surface-coatedmetal material having as a surface coating layer on the base metal, anirontitanium alloy in which a particulate matter consisting of titaniumand calcium oxide was dispersed.

Each of these metal materials obtained in this Example was subjected tothe same corrosion resistance test as set forth in Example 1, and it wasfound that even after a lapse of 60 days, these metal materials did notundergo appreciable corrosion. The thickness of the alloy layer of themetal material having mild steel as the base metal was about 0.35 mm,and an area having the particulate 'matter dispersed therein was presentbetween the surface and a point about 0.1 mm deep from the surface inthe alloy layer. In the case of the l8%Cr8%Ni stainless steel, 13%Crstainless steel, and 25%Cr-20%Ni stainless steel, the thickness of thecoating alloy layer was about 0.3 mm hardly differing'from steel tosteel. An area having the particulate matter dispersed therein existedbetween the surface and a point about 0.08 mm deep from the surface inthe alloy layer.

All of the methods used in the foregoing Examples are a kind of thepenetrating process, and therefore, the composition of the alloy layerobtained by such methods might be affected by the quality of the steelmaterial usedfFor instance, in the case of stainless steel, very minoramounts of nickel and cobalt may be contained in the layer. However, aswill be understood from the results obtained in these Examples, thecorrosion resistance does not differ depending upon the kind of thesteel material, and it is assumed that very minor amounts of componentsother than iron present in the steel material, even if incorporated inthe alloy layer, would not reduce the corrosion resistance of theresulting metal material.

As will be demonstrated by these specific Examples, the metal materialof the present invention exhibits a marked corrosion resistance againstmolten tin. In the foregoing Examples, the metal materials obtained bythe process of the invention have corrosion resistance 10 times or moreas high as that of the metal materials whose base material has beencalorized. The metal materials of the present invention which is easy towork mechanically and is low in cost have far better resistance tocorrosion than calorized iron-aluminium alloy, iron-titanium alloy andiron-aluminium-titanium alloy, and therefore the metal materials ofthe'present invention are very useful-as metals material having highcorrosion resistance against molten tin.

What we claim is:

l. A metal material having corrosion resistance against a molten metalconsisting predominantly of tin, which metal material comprises a metalbase having iron as the main constituent and a surface coating layercontaining 1 an iron alloy consisting essentially of iron and at leastone metal selected from the group consisting of titanium and aluminiumand 2 particulate matter dispersed in the alloy only in the surfaceportion of the surface coating layer, which surface portion of thesurfacecoating layer has a thickness of at least 30 and consistsessentially of 5-50 percent by weight of iron, 4090 percent by weight oftitanium, aluminium, zirconium, calcium, magnesium, strontium, barium,silicon or a mixture thereof, and 33-12 percent by weight of oxygen asoxide, the particulate matter consisting essentially of at least onemetal oxide selected from the group consisting of TiO,, A1 0,, ZrO,,CaO, MgO, SrO, BaO and SiO and at least one metal selected from thegroup consisting of titanium. and aluminium, the concentrations of thetitanium and aluminium components layer.

3. A metal material according to claim 1 wherein the diameter of theparticulate matter is predominately in the range of l0 1;. to p..

4. A metal material according to claim 1 wherein said particulate matterconsists of 15-55 percent by weight of said metal oxides and 45-85percent by weight of titanium and aluminium metals.

2. A metal material according to claim 1 wherein the portion of theparticulate matter mixed in the alloy in the surface portion of thesurface coating layer is 15 to 45 percent in terms of the percentage ofthe sectional area of the particualte matter based on the totalsectional area of the surface portion of the surface coating layer.
 3. Ametal material according to claim 1 wherein the diameter of theparticulate matter is predominately in the range of 10 Mu to 100 Mu . 4.A metal material according to claim 1 wherein said particulate matterconsists of 15-55 percent by weight of said metal oxides and 45-85percent by weight of titanium and aluminium metals.